1. Technical Field
This disclosure relates to a carbon nanotube (CNT) based thermoelectric material and a thermoelectric device using the same.
2. Description of Related Art
The thermoelectric effect is the direct conversion of temperature differences to electric voltage and vice versa. A thermoelectric material creates a voltage when there is a temperature gradient. Conversely when a voltage is applied to the thermoelectric material, it creates a temperature gradient (known as the Peltier effect). At atomic scale (specifically, charge carriers), an applied temperature gradient causes charged carriers in the material, whether they are electrons or electron holes, to diffuse from the hot side to the cold side, similar to a classical gas that expands when heated; hence, the thermally-induced current. Seebeck coefficient of a thermoelectric material measures the magnitude of an induced thermoelectric voltage in response to a temperature difference across that material.
The performance of thermoelectric devices is quantified by a figure of merit, given by ZT=S2σT/κ, where S, σ, T and κ are, respectively, the Seebeck coefficient, electrical conductivity, absolute temperature and thermal conductivity. Since Seebeck coefficient S has the square relation to the ZT value, indicating the ability of conversion between heat and electrical power, increasing the value of Seebeck coefficient is an effective way to enlarging the figure of merit of thermoelectric materials.
During the past years, great efforts have been taken to increase the efficiency of heat-power conversion. Various promising approaches have been explored to improve the figure of merit value, involving quantum-well structures, crystals with complex electronic structures, thin and multilayer films, the so-called phonon-glass/electron-crystal compound materials and so on. Among them, composites were considered not to provide any benefit because it was determined and reported that the figure merit of composites could not be any higher than the maximum one of its components through theoretical numerical simulation (I. Webman, J. Jortner, M. H. Cchen, Phys. Rev. B 1977, 16, 2959.).
What is needed, therefore, is to provide a thermoelectric composite material with a high efficiency of heat-power conversion and a device using the same.